Watch movements require drive means to supply energy to an assembly of mechanisms that serve to give at least one time indication.
In the case of mechanical watches this is a mainspring or barrel spring, which is wound by the action of a manually operated winding mechanism or as a result of the movements of the wearer that are transmitted to the barrel spring via an oscillating weight connected to a reduction wheel train. The invention relates to self-winding clockmaking movements using an oscillating weight.
The oscillating weight can wind the spring using the energy the weight produces either in a single direction of rotation only or in both directions of rotation, depending on which mechanism it is connected to.
Generally, the oscillating weight is mounted to be rotatably guided on a shaft with an unbalance. When this oscillating weight shifts in a first direction of rotation, referred to as winding direction, it drives a transmission wheel train that winds a spring of the barrel. When the weight shifts in the other direction, referred to as free direction, this oscillating weight no longer acts on the transmission wheel train of the spring and is free to rotate. In the absence of movement of the wearer the weight returns to its equilibrium point due to the unbalance after several oscillations allowing it to wind the spring each time it shifted in the winding direction.
Movement of the arm of the wearer of the watch can generate a rotation in one direction of rotation or the other of the weight to recover energy.
Self-winding devices are also known that comprise a motor intended to move the oscillating weight and enable the barrel spring to be wound. Such a device is described in document EP 0 320 754. However, the torque required for winding the spring is quite high and this involves a powerful, and therefore bulkier, motor or an also cumbersome high gear ratio.